This invention pertains to digital communication, and more particularly, is concerned with bit rate translation of a digital stream.
Current bit rate translation techniques include: i) re-sampling by interpolation and decimation processes in the digital domain; and ii) conversion of the digital signal to analog signal and back to digital signal at the new sampling rate in the analog domain.
The process of interpolation multiplies the sampling rate by an integer. The decimation process divides the sampling rate by an integer. The combination of the two processes consecutively can modify the sampling rate by any rational number. This technique requires a prior knowledge of the ratio of the two sampling rates. In some cases, it is impossible to predict timing discrepancy between digital media, particularly when the timing source has drift associated with it, such as caused by doppler shift by drifting satellites.
The digital to analog conversion and back to digital at an independent sampling rate is a technique that is inherently effective in overcoming any timing discrepancies. The technique, however, is costly because of the use of anti-aliasing filters and with high resolution analog to digital and digital to analog converters. This technique also contributes to reduction in signal to noise ratio due to additional quantization noise.
It is desirable to provide a method and an apparatus for changing the bit rate of a digitized analog signal without the need of prior knowledge of bit rates, or the need for expensive components.